Operation of pressure stills



Julie 9, 1931. E. c. HERTHEL OPERATION oF PRESSURE sTILLs Filed NOV. 21,1924 3 Sheets-Sheet 1 INVENToR Eugene '.Her/el BY Q l l y Q:

ATTORNEYS E. C. HERTHEL OPERATION OF PRESSURE STILLS June 9, 1931.

Filed Nov. 21, 1924' 3 sheets-sheet 2 ATTORNEYS June 9, 1931. E. c.HERTHEL OPERATION OF PRESSURE STILLS Filed Nov. 21, 1924 3 Sheets-Sheet3 NM, w www f'ugene C. Herel ad, QW

BY l M Y ATTORNEYS Patented June 9, -1931 v UNITED STATES 'PATENT'oFF-ice EUGENE c. HERTHEL, or CHICAGO, ILLINOIS, AssIGNon rro sINcIiAInREFINING CoM- -PANY, CHICAGO, ILLINOIS, A. CORPORATION OF I OPERATION'OFPRESSURE STILLS Application mea November 21, 1924. yserial No.751,213.

This invention' relates to improvements in the cracking of heavier,hydrocarbon oils,

such as gas o1l,for the production of lighter hydrocarbon oils, such asgasoline and pressure distillate, therefrom. The invention in-` cludesimprovements in the operation of pressure cracking stills, particularlycirculatory pressure stills, and improvements in the operation of refluxtowers employed in conjunction with pressure cracking stills;

When heavy hydrocarbons are distilled i under pressure, they are crackedwith the production of lighter oils. The products of the crackingreaction also include incondensible gases, and carbon or coke, or heavytar. In the commercial operation of a pressure still, some definiteproduct or group of products, for example gasoline or pressuredistillate, is usually desired but the vapors escaping from the stillitself may include heavier constituents in addition to ythe constituentsdesired in the pressure distillate;

and, in some cases, particularly in the distillation ot lighter chargingstocks, the escaping vapors may include vaporized constituents from thecharging stock in their original condition. The vapors frem the pressurestill are commonly subjected to a reiluxing operation to effect, to agreater or less extent, the return of such heavier vaporizedconstituents to the still for further treatment therein, but, asordinarily practiced, such methods have nevertheless resulted in theproduction of distillates containing large amounts of constituentsheavier than the desired pressure distillate. For example, in treatinggas oil for the production of gasoline by such methods, the pressuredistillate vusually includes a considerable amount of constituents ot akerosene character and others even heav/i,

er. so that it has been necessary to subject a relatively large amountof distillate to re.-

distillation to tractionate it into merchantable 'products and toseparate the heavier components. Whererefining methods involving`chemical treatment followed by redistillation have been applied to suchdistillates, this has resulted in the chemical treatment of an amount ofoil materially larger than that obtained as merchantable products.

Accordingj to the present invention, the pressure distillation iscarried out to produce a more concentrated distillate of the desiredcharacter containing an increased amount of components suitablesin thedesired products and a decreased amount of heavier constituents.

According to the present invention, a fraction including constituents ofa character corresponding to the condensed pressure distillate, isemployed for promoting and controlling in an improved manner a refluxingop-l eration to Which the vapors from the pres'- sure still aresubjected and Jr'or returning to the body ot oil in the pressure stillthe heavier constituents of the vapors unsuitable as components of thedesired pressure distillate with resulting improvement in the operationof the pressure still itself.

Whena charge of oil, such as gas oil, is subjected to a crackingtemperature in a pressure f still, cracking takes place in a gradual andprogressive manner. Lighter constituents produced by the crackingoperation' are vaporized, and other constituents, suchy as heavierhydrocarbons formed by the cracking operation, may remain and mix Withthe charge in the still. A small amountl of asphaltic or pitcho likeconstituents is also progressively formed. During the early part V ofthe operation, these pitch-like constituents may remain more or tion inthe charge, but with gradual and progressive cracking the amount of suchconstituentsl gradually and progressively increases until the amount ofsuch constituents increases beyond the saturation point when lesscompletely in soluof oil decreases while the amount of pitchlikeconstituents increases until finally deposition of pitch-likeconstituents occurs.

In a prior application filed July 12,4922, Serial No. 574,380, there isdescribed an improved process of cracking hydrocarbon oils according towhich the concentration of pitch-like constituents in the charge iscontrolled during the operation of the pressure still by withdrawingpitch-laden tar and introducing freshcharging stock at a regulated rateto maintain the pitch content of the charge below the saturation point.ln one aspect, the present invention involves a further improvement uponthe process described inthis prior application, and similarly mayinvolve carrying out the cracking operation with the introduction offresh charging stock and the withdrawal of pitch laden tar'to maintainthe pitch content of the charge below saturation.

According to the present invention, the vapors from the pressure stillare subjected y to a refluXing operation in direct contact with an oilheavier than the desired pressure dis" tillate but includingconstituents corresponding in character to the desired pressure'distillate. The lighter constituents of this oil employed to promotethe'reflu'xing operation are more or less completely vaporized bycontact with the vapors from the still and the cooling eiect of thevaporization effects a ,i sharp reiuxing of the heavier vapors,particularly of the constituents heavier than the vaporizedconstituents. ln this way, by regulating the amount and character of therefiuxing oil introduced into direct contact with the vapors from thestill, a sharp fractionation between the components suitable in thedesired pressure distillate and the heavier components can be effected,and the character of the pressure distillate as well as of the refluxedconstituents can be more or less closely controlled. The intermediatelighter vapors, heavier than the desired pressure distillate, which areallowed to escape with the pressure distillate, in ordinary methodsy ofoperation,

are returned to the pressure still from which they have escaped wherethey assist in maintaining the concentration of pitch-like constltuentsproduced during t-he progress of the cracking operation below thesaturation point in the still charge. l

In the process of the present invention,ac cordingly, the pitch contentof the charge of oil in the pressure still may be controlled bywithdrawing pitch-laden tar and introducing fresh charging stock inregulated amount while at the same time the light intermediateconstituents which usually escape from the still with and form a part ofthe pressure. distillate although too heavy to be suitable as componentsof the desired products alie refluXed to the still charge.

The oil employed for promoting and conuents corresponding in characterto constituents of the desired distillate may be employed. Where theoperation is carried out with the introduction of additional freshheavier charging stock, the oilemployed for promot- I ing andcontrolling the refluXing operation may also be introduced into directcontact with the vapors from the still in admixture with all or a partof this additional fresh charging stock. .0r, the oil employed forpromoting and controlling the refiuxing operation may be introduced nearthe upper end of a reflux tower through which the vaporsl from thepressure still are passed upwardly and all or a part ot the'I heaviercharging stock introduced into the tower at some intermediate point.

As compared to ordinary methods of operation, the introduction intodirect contact with the vapors in the reflux tower of an oil heavierthan the desired pressure distillate but including a large amount ofconstituents corresponding to the constituents l,of the desired pressuredistillate and the consequent Vaporization of this large amount oflighter constituents from the introduced oil and refluXing of theheavier intermediate constituyents from the still may result, where the`operation is carried out to produce a very light fraction, in theconsumption of an eX- cessive amount of heat in revaporizing in a cyclicmanner these intermediate constituents with the resulting decrease inthe rate of cracking. This decrease in the rate of cracking may also beaccompanied by an inability on the part of the still to maintain,autogenously, the Vdesired pressure due to the decreased rate ofproduction tot cracked vapors and fixed gases. ln carrying out theprocess of the present invention, these conditions may be offset, ifencountered, in any one of several ways. For this purpose, the stillpressure may-be maintained by the introduction rof an, vextraneous gas,or the still pressure may be reduced and regulated at\ a point betweenthe still and the condenser. By operating the v pressure lstill Tineither of these ways, the proper still pressure can be maintained alagreater orless extent, the revaporiz'ation of these intermediateconstituents before they are further cracked. rlhe operation of therefluxtower may also be regulated so that the pressure distillateescapingincludes a somewhat increased amount ofthe lighter of theseintermediate constituents which tend to be rec cled to an excessiveextent between the the still. Where a circulatory pressure stillisemployed, in which theoil is circulated from and to a bulk supply tankthrough a heater in which it is heated to the cracking temperature, thereflux from the refluxing operation may be returnedto the still in amanner such that it is directed through the heater with a .circulatingoil, or-a positive forcing means, such as a pump, may be employed topositively circulate the reflux through 'the heater, so that it exerts asolvent action in the heater and is subjected to the crackingtemperature therein.

The refluxing operation of the present invention may, with particularadvantage, be carried out in a heat insulated reflux tower so 'that heatexchange is conn'ed to the conv stituents indirect contact in the tower,there- .by promoting heat economy, by preventing loss of heat to theairor other external cool'- mg medium, permitting closer regulation andcontrol of the refluxing operation, and effecting a maximumfractionation of the vapors from the still.

While the refluxing operation of the pres- Imt invention may be carriedout in reflux towers of various types, itis carried out with particularadvantage in a reflux tower of baffle construction having a relativelylarge area for free passage of the vapors therethrough. Atower of thistype offers important advantages in safety and in ease of control, isreadily repaired, and has other advantages which will further appear;

The invention will be further described and illustrated in connectionwith the accompany-- Y ing drawings which show, in a somewhatdiagrammatic and conventional manner, severalforms of pressure stillsladapted for the practice of the processof the invention; but it isintended and will be understood that the invention is not limited to thespecific methods of operation so described.

In the 4accompanying drawings the three figures represent, in elevationand partly -in section, similar views of three arrangements of pressurestills adapted for the practice of the process of the invention. Thedrawings are not intended to be to scale, for example, the distillatetanks and charging stock tanks illustrated may be materially larger inactual practice than is shown by the proportions of the drawings.

While the process of the invention may be carried out vin pressurecracking stills of different types, it is of special value andapplication in connection with circulatory pressure stills of .thecharacter illustrated. This pressure cracking still is of the generalconstruction and operation described and illustrated in United StatesLetters Patent No. 1,285,200 granted to the Sinclair Refining CompanyNovember 19, 1918 on the application of Edward lV. Isom.

The pressure still illustrated is made up of the bulk supply tank 5located away from the heating furnace, the vertically arranged heatingtubes 6 located in the heating flue of the furnace, and circulatingpipes 7, 8 and 9 connecting successively the bulk supply tank, acirculating pump 10, thelower end 'of the heating tubes, and the upperend of the heating tubes and the bulk supply tank. A. circulating pumpmay, with advantage, be employed for circulating the oil from the bulksupply tank through the heating tubes and back to the bulk supply tank;or the circulating pump may be omitted and thermosyphonic action reliedupon forsmaintaining circulation but with decreased still capacity.Arranged above the bulk supply tank 1s a reflux tower 11 having a seriesof baflles therein and connected with the vapor\ s dome of the bulksupply tank through the vapor line 12; The vapors from the top of thereflux tower escape through a vapor line 13 to a condenser 14 arrangedto discharge into the receiver 15. From the receiver, the condenseddistillate is discharged through valved connection 16 and theuncondensed vapors and gases through the valved connection 17. 'Aconnection 18 is provided at the lower part of the circulatingconnections of the still for pumping out and charging the still, andatar draw-olf connection for-use during the operation of the still isprovided at 19. A connection 20 is also arranged for introducing freshcharging stock into the circulating oil through-the bearings of thecirculating pump. lVhere no circulating pump is employed this connectionmay be arranged to discharge directly into the circulating conneetionsIof the still, advantageously in the connection for circulating oil fromthe bulk,

ployed for maintaining the still pressure, the

gas pressure may be applied through connecflux tower, and through itinto direct contact with the vapors in the reflux tower. This `pump isarranged tol draw distillate from the separate distillate tank 25. Aconnection 26 is provided for returning reflux, and any unvaporizedconstituents of the oil introduced into-the reflux tower, to thecirculating connection 7 on the suction side of the circulating pump 10.The reflux tower is advantageously provided with a heat insulatingjacket (not shown) of suitable material, such as asbestos or mineralwool; yand the other exposed parts of the pressure still may also withadvantage be covered with heat insulating material to preventunnecessary heat loss and to promote heat economy. A pump 27 is arrangedto force fresh charging stock from any suitable source into the pressurestill through connections and the bearings of the circulating pump.

In carrying out the cracking process of the present invention in theapparatus illustrated in Fig. l, the still is charged with freshcharging stockin the usual way, for example through connection 18, andbrought to the cracking temperature and pressure in the usual manner.`The charging stock, for example, may be gas oilorv other suitablecharging stock which is to be cracked for the production of gasoline orpressure distillate. The pressure maintained inthe still during thecracking operation can vary, de-

pending upon the-character of the charging s/tock and otherconsiderations. For example, with a gas oil charging stock and for theproduction of gasoline a pressure up to 125 lbs. per sq. inch or morecan be used. After cracking conditions of temperature and pressure arereached, cracking-begins and takes place in a gradual and'progressiveIna-nner, the vapors liberated in the still proper escaping and passingupwardly through the reflux tower. At this point, or shortly thereafter,the Aintroduction through connection 22 of an oil containing a largeamount of constituents Corresponding to thel constituents of the desiredpressure distillate from a separate source, such as tank 25, 1s begun.As the distillation proceeds,

the still charge is maintained by the intro,

duction of additional charging stock, for example gas oil, through thebearings of the circulating pump; and before the pitch content; of thecharge reaches the saturation point, the withdrawal of tar throughconnection 19 is begun and the rate of tar drawoff -and of freshcharging stock feed is regulated to maintain the pitch content of thecharge below the saturation point.. i

The lighter portion of the oil introduced into the reflux tower isvaporized to a greater or less extent by heat exchange with the vaporsfrom the still and the heavier constituents of the vapors are reuxed bythe cooling effected by the vaporization. lhe extent towhich therefluxing oil is vaporized depends in large part upon the character ofthe refluxing oil. Since the constituents of the reuxing feed which arevaporized correspond in character to the desired distillate, heaviercomponents are not introduced into the distillate to any great extent byemploving such a feed as a refluxing medium. t the same time, a sharpfractionation is effected and the constituents of the vapors heavierthan the vaporized'constituents of the feed introduced into the refluxtower are refluxed and returned to the still through connection 26together with the unvaporized constituents of the oil introduced intothe. reflux tower. As compared to an operation in which heavier chargingstock is employed alone as a refluxing agent, however, the lighter feedfor promoting and controlling the rcfluxing` operation yhas a reducedtendency to carry back to the still constituents suitable as componentsof the desired pressure distillate. As is shown in the drawing, therefluxis returned to the suction side of the circulating pump so that itis redirected through the heating tubes where it is subjected to thecracking temperature in admixture with the circulating oil in the stillbefore being introduced into the main body of oil in the still or beforeit can again escape from the4 still proper as a vapor. rlhe refluxedconstituents are thus returned and admixed with the circulating stillcharge where they assist in maintaining pitch like constituents insolution and where they are subjected to further cracking. F or example,in the production of a 450 F. end-point gasoline and with a feed to thereflux tower comprising a major part of gasoline constituents boilingbelow 450 F., a major part of the constituents of the vapors from thestill boiling between about 450 F. and 500o l?. and substantially all ofthe heavier vapors can be refluxed to the still, and, by properregulation, a gasoline character fraction can be directly produced. rlherefluxing operation, however, may be regulated so that a pressuredistillate including a larger amount of heavier components is produced.

The followingis an example of the prac- .tice of the present inventionas carried out in a still of the character just described:

rlhe still was charged with 10,000 gallons of gas oil charging stock.rIhe still charge was heated, drips were taken off, and the charge wasbrought to a working pressure of about 125 pounds per square inch. Thestill was then opened to the .condenser and the distillate began to passover. At about the same time the introduction of a distillate includingabout 50% of 450o F. end-point gasoline into the reflux tower was begunwhile additional gas oil charging stock was introduced through the pumpbearings. Before the pitch-content of the charge reached the saturationpoint, the withdrawal of tar was begun and continued throughout theremaining portion of the run. The rate of tar drawo' and gas oil feedwere regulated to maintain asubstantially constant still charge. In thisrun additional gas oil to the amount of 21,210' gallons was fed into thestill during the operation, 19,820 gallons of distillate were introducedinto the reflux tower, and 16,345 gallons of tar were withdrawn, thetotal distillate amounting to 25,970 gallons.

l This distillate included 22,070 gallons, or

about 85%, of 450 F. end-point gasoline, or the net gasoline productionwas 12,160 gallons. The run lasted 26%c hours and during this timecirculation in the still was maintained at the rate of about 2,000gallons per minute.

In another run, the still was charged with 10,000 gallons of gas oil andbrought to a working pressure ofv about 125 pounds per square inch, thetotal period of operation bein 29 hours. During this time, additionalgals oil to the amount of 22,770 gallons was ntroduced through the pumpbearings, 23,- 520 gallons of a distillate including 50% of 450o` F.end-point gasoline was introduced into the tower, 18,012 gallons of tarwere withdrawn to inhibit increase in the concentration of pitch in thestill charge, and a dis-` tillate of 28,300 gallons was produced. Thisdistillate included 24,050 gallons, or about 85%, of 450o F. end-pointgasoline,^or the net gasoline production was 12,290 gallons.

While the invention is of particular advantage in connection withprocesses in which the concentration of pitch-like constituents inthestill charge is controlled by the regulated introduction of chargingstock and withdrawal of tar, certain advantages of the invention in theoperation of a circulatory pressure still of the type just described areobtained in a batch operation, that is in an operation in which no taror only a relatively small amount of tar is withdrawn. In particular,the return of intermediate constituents to the oil circulating throughthe heating tubes by the improved refluxing operation of the inventionincreases the solvent effect of the still charge where the oil issubjected to the highest temperatures and assists in reducingithedeposition of pitch-like constituents upon the heating surfaces of thestill. Such an operation can be carried out with or without theintroduction of fresh charging stock during the progress of theoperationz where fresh charging stockis so introduced it further assistsin maintaining pitch-like constituents formed by the cracking operationin solution in the charge.

In the apparatus illustrated in Fig. 2 similar parts are designated bythe same reference numerals with the distinguishing character a appendedthereto. The apparatus illustrated in Fig. 2 di'ers in construction andoperation Ifrom that shown in Fig. 1 principally in the arrangement ofthe means for introducing fresh charging stock during the progress ofthe cracking operation and in the provision of a pump for positivelyforcing reflux and admixed feed oil through the heating tubes with thecirculating oil in the still proper.

In addition to the connection 26a for returning reflux to the suctionside of the cir-- culating pump 10a, connections 29 and 30 and pump 31are arranged for positively forcing reflux from the reflux tower intothe oil circulating to the heating tubes in the still through the lowercirculating connection 8a. Valves 29 and 26 provide for the direction ofthe reflux either through the reflux circulating pump 31 or through theoverflow connection 26a as may be desired.

Pump 21a is arranged to force distillate containing a large amount ofconstituents corresponding to the constituents of the desired pressuredistillate from any suitable source delivered through connection 34,into the upper end of the reflux tower through sprayhead 33 andconnection 32. rlhe pump 28 is arranged to forc'e additional fresh heavycharging stock from the supply tank 35 into the pressure still throughconnection 20a and the bearings of the lcirculating pump 10a, into thereflux tower at an intermediate point through the sprayhead 36 andconnection 37, or'into the upper end of the reflux tower throughconnections 38 and 32. The heavier charging stock may be introduced intothe still through one or more of these channels at the same time andvalves 20', '37- and 38 are provided in the respective connections tocontrol and regulate the distribution of the additional heavy chargingstock.

In one way of carrying out the process of the invention in the apparatusillustrated in Fig. 2, the heavier charging stock may be introduced'intothe reflux tower at an intermediate point through connection 37 and thelighter oil for controlling and regulating the refluxing operationintroduced into the upper part of the reflux tower so that the finalseparation between the heavier constituents and the constituentssuitable as components of the desired pressure 'distillate is effectedin the upper-part of the tower above the point of introduction of theheavier feed. Or, all or a part of the heavier charging stock introducedinto the reflux tower may be introduced intothe upper end of the towerin admixture with the lighter oil for controlling and regulating therefluxing operation, in

` mixture will be vaporized in the reflux tower,

promoting and controlling the refluxing operation in a manner similar tothat which has been described.4 In addition to the heavier chargingstock introduced into the reflux tower, additional heavy charging "stockmay be forced into the pressure still through the bearings of thecirculating pump, or at some other point where it does not contact withthe vapors escaping from the still. To the extent that the heaviercharging stock is introduced into direct contact with the vapors in thereflux tower,fit assists in promoting the refluxing operation and isthereby preheated. A somewhat more effective separation of the lheavierconstituents may be effected, however, by introducing the major part ofthe heavier charging stock introduced into the tower at an intermediatepoint and by introducing the lighter oil for controlling and regulatingthe refluxing operation into the upper part of the tower.

The reflux from the reflux tower may be returned through connection 26aand admixed with the oil circulating from the bulk supply tank to theheating tubes as has been described in connection with Fig. .1; or thereflux may with advantage be positively kforced into the oil circulatingthrough the heating tubes by pump 3l so that it is subj ected to thecracking temperature in admixture with the circulating still charge inthe heating tubes before it is returned vto the main body of oil in thebulk supply tank or before it can escape as a vapor therefrom. Thereflux is thus compelled to circulate through the heating tubes inadmixture with the circulating pitch-containing oil so that it assistsin preventing the deposition of pitch upon the heatingsurfaces and so'that it is necessarily subjected to the cracking temperature in theheating tubes. v

f In the apparatus illustrated in Fig. 3 the same parts are designatedby the same reference numerals with the distinguishing character oappended thereto. Tn this modified form ofthe apparatus an auxiliaryheating coil 39 is arranged in the heating flue of the furnace betweenthe fire-box and the vertical heating tubes so that the auxiliary coilis subjected to the hottest heating gases and the 4main heating tubes tothe tempered heating gases which have passed over the auxiliary coil.This auxiliary coil is arranged so that the reflux from the refluxtower, either with or without the admixture of fresh charging stock, iscirculated therethrough, thus subjecting the reflux to the hottestheating gases and 'at the same time protecting the heating surfaces overwhich the pitch containing c rge of oil in the still proper iscirculated.

For this purpose an auxiliary tank or reservoir 40 is arranged toreceive the reflux moat-273 from the reflux ltower through connection41. This tank or `reservoir has a vent pipe 42 leading back to thereflux tower. A valved connection 43 is also provided for dischargingreflux from the reflux tower directly into f the bulk'supply tank 5b.The tank 40 is also connected through the pipes 44 and 45 to the feedline of the auxiliary coil. A pump 46 is arranged to pump the oil fromthe tank 40 through the auxiliary coil, while the connecting pipe 47permits circulation by gravity and by convection when the pump 46 is`not used. A branch pipe 48 leads from connection 44 to the bottom ofthe bulk supply tank for supplying additional oil in case the amount ofreflux is insufficient to maintain full the auxiliary coil. A connection49 is also provided for circulating fresh charging stock through theauxiliary coil if desired. A connection 5l is arranged between the.inlet 45 of the auxiliary coil and the dis-' charge side of thecirculating pump 10b, andy may be used in starting the still inoperation as well as in draininothe auxiliary coil and connection pipingwhen the still is pumped out. The auxiliary coil 39 is arranged todischarge through connection 52 into the returnl circulating Vconnection9b to the bulk supply tank.

The auxiliary reservoir or tank 40 is shown `as located within the bulksupply tank 5b, althoughv it is not in open communication therewithexcept through'the pipe connections. This location of the auxiliaryreservoir is not essential but it is convenientand enables a tankconstruction to be used which v does not need to withstand high pressureas the pressure inside andl out is approximately the same. l j

Tn carrying out the process of the invention in the'apparatus'illustrated in Fig. 3, the reflux tower maybeeoperated inmuch the same way as has been described inconnection with Figsl and 2. fAlighter oil for controlling andregu'lating the refluxing operation.

is introduced into the upper end of the tower, and additional heaviercharging ystock may be introduced into the pressure still through thebearings of the circulating pump, into the reflux tower at anintermediate point, into the upper end of the reflux tower in admixturewith the lighter oil, or through two ory of reflux is for any reasoninsuflcient to maintain full the auxiliary coil, additional oil issupplied thereto either from the bulk'supply Cil tank through connection48, from the circulating connections through connection 51, or from anexternal supply through conbe forced through the auxiliary. coil throughconnection 49 to assist in absorbing heat from the hottest heating gasesto further protect the main heating surfaces ofthe still proper.

In carrying out the process of the present invention for the productionof a gasoline character distillate from a heavier hydrocarbon oil, adistillate containing ai gasoline fraction which it is desired to blendwith the preswithv thehot vapors therein and at the same l time refluxto the still the heavier constituents of the vapors. The gasolineconstituents of the fraction are thus employed to promote and controlthe refluXing operation while at the same time they escape with -thepressure distillate and are condensed therewith so that i the blendingoperation is carried outin an improved manner.

One of the important advantages of the invention is that it enables theproduction of a pressure dist'illate containing the desired constituentsin increased concentration. This enables a marked reduction in the costof refining the pressure distillate, for example in the furthertreatment of the pressure-distil-- late for the production of a finishedgasoline therefrom, in that the amount of pressure distillate it isnecessary to handle per gallon of desired products is materiallyreduced. Less equipment is required both for chemically .treating andfor redistilling the distillate,

and the cost oflabor, chemicals and fuel for such further treatment isAalso reduced. The distillate is also relatively free from heavy ortarryconstituents of the fresh oil or still charge and the amount ofheavier constituents inthe pressure distillate which may tend l to carrywiththem objectionable impurities or otherwise interfere with therefining operations is reduced, further facilitating the refiningtreatment. The process of the presentl invention also enables theproduction of an increased amount of gasoline, of the desired pressuredistillate, due in part to the better fractionation edected in thereflux tower on the pressure still and in part to a reduction of theamount of gasoline constituents returned to thepressure still with thereflux and subjected to further crackingtherein. One evidence indicatinga decrease in overcracklng of constltuents sultable as nection 49.Additional fresh oil mayffalsocomponents of the desired ldistillate is adecrease in the production of fixed gas. In one case, the amount offixed gas produced per hundred gallons of charge was reduced to 18 to Q0pounds as compared to 21 to 22 pounds with the ordinary method ofoperation. Another important advantage of the invention is that itenables the production of an increased yield of gasoline or pressuredistillate on Ithe oil charged to the still. Due to theV improvedseparation effected in the reflux tower, `less of the pressuredistillate constituents' are reluXed to the still and the amount of lconstituents heavier than the desired pressure distillate escaping withthe pressure distillate is also reduced. In the production of gasolinefromgas oil, for example, the amount of fresh charging stock introducedduring the progress of the cracking operation can be reduced by anamount corresponding to the amount of gas oil ordinarily removed withthe pressure distillate, and the heat ordinarily used in preheating thisamount of gas oil to the cracking temperature can be employed ineffecting the cracking operation. The `amount of heat 'ordinarily usedto revaporize in the still pressure distillate constituents returned tothe still, and in some casesv in further cracking them, can also beapplied to the cracking operation. A more concentrated application ofthe heat to the cracking of the pressure still charge is thus obtained.As compared to ordinary methods of operation in which constituents whichmight be further cracked to produce additional /lgasoline escape withthe distillate and in which gasoline constituents are" refluxed andovercrackcd the yield of gasoline on the gas-oil charged to the stillmay be increased from 2 to 6% or more. An important economy may also beveected in the amount of cooling water, or of other cooling medium,required for cooling and condensing v the pressure distillate due to theconcentration of the pressure distillate, and the size of the condenseremployed may be correspondingly reduced. rl`hese factors may also assistin making possible a material saving of fuel.

The process of the present invention also has important advantages asapplied to the direct production of a gasoline character distillate inthe ease of control which it adords and in the simplicity of theoperation. Moreover, in carrying out the present invention, a redux`tower of ordinarybafiie construction may be employedwith advantage.:Such a tower does not materially restrict the escape of vapors from thestill and a relatively large area for their free escape is providedthereby reducing any danger due to sudden generation of vapors.Likewise, the path of the vapors through the tower isrelatively shortand the heat exchanging relations maintained between the constituentslin a reflux tower of the baffle type are comparatively simple aordingdirect and substantially iinmediate control. A single tower of this typeis, moreover, adapted to produce a wide range of products by appropriatecontrol of the refluxing operation carried out therein. While variousfeatures of the process which have been described may be employedconjointly with particular advantage, for example, while the refluxingoperation may be carried out in a heat insulated reflux tower of bailleconstruction employed in conjunction with a circulatory pressure stillwith directed return of the reflux with the oil circulating to andthrough the heater, it willbe apparent that certain novel features ofthe invention may be employed alone with advantage, and that manyfeatures of the process of the invention can be carried out in other anddifferent types of pressure still systems. I have endeavored todefinethe invention in the subjoined claim and to distinguish it fromthe prior art so far as known to me without, however, rclinquishing or`abandoning any portion or feature thereof.

claim:

An improved method of cracking hydrocarbon oils, which comprisesheatinga body of the oil to a cracking temperature under pressure in apressure still, passing the vapors from the still upwardly through areflux tower, passing uncondensed jva-pors from the reflux tower to `acondenser to produce a distillate, introducing an oil heavier than saidf distillate andlincludinga substantial quantity of Constituentscorresponding in characi n C ter to constituents of the distillate intodirect contact with the vapors in the upper end of the reflux tower,introducing ya heavierv oil Ainto direct contact with thefvapors at anintermediate point in the re-lux tower, and re` `turning reflux withoutsubstantialV cooling from the tower to the still.

In testimony whereof I aflix my signature.

EUGENE C. HER'llll-IEL,

